add xml file of datasets for masterclasses from docdb

We should also add "date" fields to every record, like:

```xml
    <datafield tag="260" ind1=" " ind2=" ">
      <subfield code="b">CERN Open Data Portal</subfield>
      <subfield code="c">2014</subfield>
    </datafield>
```

Also, do we have any information about dataset size (`256`) and other fields like CMS SW version, selection, validation etc?  We could always add these later after merge as well.